This invention relates to thermocouple assemblies and particularly those that are used inside lubricated components such as turbine bearings. Specifically, the invention relates to a unique insulating jacket and thermocouple lead arrangement which prevents leakage of lubricating medium through the thermocouple jacket.
During the installation and routing of a thermocouple in, for example, a gas turbine bearing housing, the insulating jacket of the thermocouple can be cut or skinned. Any opening in the insulation jacket during installation permits lubricant such as oil within the bearing housing to leak through the outer insulating jacket and along the internal wires or leads. The oil can flow all the way to a junction box where the thermocouple leads are connected to terminal boards. The oil leakage may even be sufficient to flood the board and cause malfunction of the thermocouple readings. While this problem can be fixed easily if the opening in the insulation jacket is located outside the bearing housing, repair proves problematic in the event the cut or tear is inside the bearing housing, requiring an expensive and time consuming teardown of the bearing and attendant shut-down of the turbine.
This invention solves the problem of internal leakage of fluid through the thermocouple insulating jacket by introducing a silicone (or other epoxy) xe2x80x9cpseudo-wirexe2x80x9d into the assembly process during manufacture of the thermocouple. The xe2x80x9cpseudo-wirexe2x80x9d (preferably silicone) extends through the insulated jacket along and among the thermocouple leads. The thermocouple is then locally heated to a temperature which melts the silicone wire inside the thermocouple jacket and fuses it to the inside wall of the jacket. These localized fused areas may be about 12 inches in length and spaced apart by intervals of about 24 inches. Each of these fused areas provides a blockage to potential oil leaks caused by a cut or tear in the outer insulating jacket of the thermocouple.
Accordingly, in its broader aspects, the present invention relates to a thermocouple assembly comprising a thermocouple; a plurality of lead wires extending from the thermocouple; an insulating jacket extending along and enclosing the plurality of leads; and at least one internally sealed area within the insulating jacket to prevent fluid leakage along and within the insulating jacket.
In another aspect, the invention relates to a machine component housing having a lubricant therein and a thermocouple assembly mounted in a wall of the housing, the thermocouple assembly comprising: a thermocouple; a plurality of lead wires extending from the thermocouple; an insulating jacket extending along and enclosing the plurality of leads; and at least one internally sealed area within the insulating jacket to prevent fluid leakage along and within the insulating jacket.
In still another aspect, the invention relates to a method of preventing leakage of a fluid along and through an insulating jacket of a thermocouple comprising the steps of: a) attaching a plurality of lead wires to a thermocouple; b) adding a heat sensitive pseudo-wire to extend along the plurality of lead wires; c) enclosing the lead wires and pseudo-wire inside an insulating jacket; d) locally heating axially spaced portions of the insulating jacket to a temperature which melts the pseudo-wire and fuses it with an interior surface of the jacket.